The focus of this study was to compare the yolk flavor of eggs from laying hens of Chinese indigenous and commercial, based on detection of volatile compounds, fatty acids, and texture characteristics determination, using sensory evaluation, artificial sensors (electronic nose (E-nose), electronic tongue (E-tongue)), and gas chromatography-mass spectrometry (GC-MS). A total of 405 laying hens (Hy-Line Brown (n = 135), Xueyu White (n = 135), and Xinyang Blue (n = 135)) were used for the study, and 540 eggs (180 per breed) were collected within 48 h of being laid and used for sensory evaluation and the instrument detection of yolk flavor. Our research findings demonstrated significant breed differences for sensory attributes of egg yolk, based on sensory evaluation and instrument detection. The milky flavor, moisture, and compactness scores (p < 0.05) of egg yolk from Xueyu White and Xinyang Blue were significantly higher than that of Hy-Line Brown. The aroma preference scores of Xinyang Blue (p < 0.05) were significantly higher, compared to Hy-Line Brown and Xueyu White. The sensor responses of WIW and W2W from E-nose and STS from E-tongue analysis were significantly higher foe egg yolks of Hy-Line Brown (p < 0.05), compared to that of Xueyu White and Xinyang Blue. Additionally, the sensor responses of umami from E-tongue analysis, was significantly higher for egg yolks of Xueyu White (p < 0.05), compared to that of Hy-Line Brown and Xinyang Blue. Besides, the contents of alcohol and fatty acids, such as palmitic acid, oleic acid, and arachidonic acid, in egg yolk were positively correlated with egg flavor. The texture analyzer showed that springiness, gumminess, and hardness of Hy-Line Brown and Xueyu White (p < 0.05) were significantly higher, compared to Xinyang Blue. The above findings demonstrate that the egg yolk from Chinese indigenous strain had better milky flavor, moisture, and compactness, as well as better texture. The egg yolk flavors were mainly due to presence of alcohol and fatty acids, such as palmitic acid, oleic acid, and arachidonic acid, which would provide research direction on improvement in egg yolk flavor by nutrition. The current findings validate the strong correlation between the results of egg yolk flavor and texture, based on sensory evaluation, artificial sensors, and GC-MS. All these indicators would be beneficial for increased preference for egg yolk flavor by consumers and utilization by food processing industry, as well as a basis for the discrimination of eggs from different breeds of laying hens.

The decline in eggshell quality resulting from aging hens poses a threat to the financial benefits of the egg industry. The deterioration of eggshell quality with age can be attributed to changes in its ultrastructure and chemical composition. Specific matrix proteins in eggshells have a role in controlling crystal growth and regulating structural organization. However, the variations in ultrastructure and organic matrix of eggshells in aging hens remain poorly understood. This study assessed the physical traits, mechanical quality, chemical content, as well as the microstructural and nanostructural properties of eggs from Jing Tint 6 hens at 38, 58, 78, and 108 wk of age. Subsequently, a quantitative proteomic analysis was conducted to identify differences in protein abundance in eggshells between the ages of 38 and 108 wk. The results indicated a notable decline in shell thickness, breaking strength, index, fracture toughness, and stiffness in the 108-wk-age group compared to the other groups (P < 0.05). The ultrastructure variations primarily involved an increased ratio of the mammillary layer and a reduced thickness of the effective layer of eggshell in the 108-wk-age group (P < 0.05). However, no significant differences in eggshell compositions were observed among the various age groups (P > 0.05). Proteomic analysis revealed the identification of 76 differentially expressed proteins (DEPs) in the eggshells of the 38-wk-age group and 108-wk-age group, which comprised proteins associated with biomineralization, calcium ion binding, immunity, as well as protein synthesis and folding. The downregulation of ovocleidin-116, osteopontin, and calcium-ion-related proteins, together with the upregulation of ovalbumin, lysozyme C, and antimicrobial proteins, has the potential to influence the structural organization of the eggshell. Therefore, the deterioration of eggshell quality with age may be attributed to the alterations in ultrastructure and the abundance of matrix proteins.

The decline in eggshell quality with increasing hen age may be related to changes in ultrastructure and chemical composition, with matrix proteins playing key roles in these changes. However, research on blue-shelled eggs remains limited. This study investigated the effects of hen age (35, 55, 75, and 85 weeks) on the physical, mechanical, and chemical properties of eggshells in the Xinyang blue-shelled laying hens, as well as their ultrastructural and nanostructural characteristics. Subsequently, a comparative proteomic analysis was performed to elucidate the differential protein profiles in eggshells from hens at 35 and 85 weeks of age. Results showed that egg weight, eggshell weight, and eggshell surface area increased with hen age, whereas eggshell stiffness decreased (p < 0.05). As the age advanced, the eggshell organic matter content declined (p < 0.05). The effective layer ratio, mammillae density, as well as the porosity and total pore area in the mammillary layer also decreased with age, whereas the ratio of the mammillary layer increased (p < 0.05). Compared to eggshells collected from 35-week-old hens, those from 85-week-old hens showed increases in egg weight, eggshell weight, surface area, and both the ratio and thickness of the mammillary layer (p < 0.05). However, significant decreases were observed in eggshell stiffness, organic matter content, phosphorus content, effective layer ratio, mammillae density, as well as the porosity and total pore area in the mammillary layer (p < 0.05). Additionally, eggshell stiffness, phosphorus content, and organic matter content were significantly correlated with each other (p < 0.05). Proteomic analysis identified 37 downregulated and 68 upregulated differentially expressed proteins (DEPs, FC > 1.2 or < 0.83, with a p-value < 0.05) in eggshells from 85-week-old hens compared to those from 35-week-old hens. These DEPs are associated with functions such as biomineralization, calcium transport, immunity, and proteases and protease inhibitors. Mantel and Pearson correlations suggest that these functions may be involved in regulating eggshell stiffness, phosphorus content, and organic matter content. Overall, the eggshell stiffness decreased from 35 to 85 weeks of age, which may be attributed to the reductions in eggshell organic matter and phosphorus contents, as well as the deteriorations in eggshell ultrastructure. The proteins associated with biomineralization, calcium transport, immunity, and proteases and protease inhibitors may contribute to these changes.

Food Science of Animal Resources (Food Sci. Anim. Resour.) is an international, peer-reviewed bimonthly journal publishing original research and reviews on basic and applied aspects of the use of animal resources including the meat, egg, dairy, and edible insect/worm products. Food Sci. Anim. Resour. is published and distributed by the Korean Society for Food Science of Animal Resources.